Actuator position control systems are useful in cameras and photographic printers for exposure control by control shutter aperture opening and closing. It is known to use closed loop shutter controls for this purpose. Such control require a consistent feedback control that must be insensitive to temperature, humidity and long term drift conditions. Current types of control systems rely on sensor stability to maintain exposure accuracy. These are precalibrated during manufacture and must be manually recalibrated as part of a periodic maintenance service routine as the camera or photographic printer ages in order to maintain the necessary exposure accuracy. It is desirable therefore to provide actuator position control systems for camera and photographic printer shutters and similar apparatus which are automatically self-calibrated and avoid the need for manual recalibration as part of periodic service routines to maintain accurate and reliable of operation.